E. coli O157:H7, an important human pathogen causing hemorrhagic colitis and hemolytic uremic syndrome, has been reported with increased frequency during the past decade as a cause of human illness [for reviews, see Bell, P. B. et al. (1994) JAMA 272:1349-1353; Griffin, P. M. et al. (1991) Epidemiol. Rev. 13:60-98; Padhye, N. Y. et al. (1992) J. Food Prot. 55:555-565]. Cattle, especially young animals, have been implicated as a principal reservoir of E. coli O157:H7, with undercooked ground beef being a major vehicle of foodborne outbreaks. Also, the number of fruit-, fruit juice-, vegetable- (lettuce) and water- (including recreational lakes) related outbreaks have increased dramatically in recent years.
A recent national survey performed by the USDA National Animal Health Monitoring System revealed that 1.6% of feedlot cattle fecally shed E. coli O157:H7 and 0.4% shed E. coli O157:NM [Dagatz, D. (1995) USDA:APHIS:VS, Centers for epidemiology and animal health. Fort Collins, Colo. (personal communication)]. A major study of calves on dairy farms revealed that 1.5% that were between the age of weaning and 4 months shed E. coli O157:H7 in their feces [Zhao, T. et al. (1995) Appl. Environ. Microbiol. 61:1290-1293]. Experimental infection of calves and adult cattle with E. coli O157:H7 varies widely among animals of the same age group, but persists longer in calves than in adults and previous infection does not prevent reinfection by the same strain of E. coli O157:H7 [Cray, C. W. et al. (1995) Appl. Environ. Microbiol. 61:1585-1590]. Other animals, such as chickens, deer, and sheep have also been determined to have the ability to carry E. coli O157:H7 for an extended period of time.
Many public health concerns have been raised regarding E. coli O157:H7 contamination of foods. Such concerns have been heightened by the unique acid tolerance of E. coli O157:H7. Proper cooking is an effective method to kill E. coli O157:H7 in foods. However, unsanitary practices in preparing foods often result in foodborne illness, hence methods to reduce or eliminate carriage of E. coli O157:H7 in cattle are needed to reduce the public's exposure to the pathogen in food and the environment [Wang, G., et al. (1996) Appl. Environ. Microbiol. 62:2567-2570].
Vaccination has been the traditional approach to protecting cattle from carriage of harmful bacteria. However, E. coli O157:H7 does not adhere to or infect cattle. The primary sites of E. coli O157:H7 localization in calves are the rumen and colon. The rumen appears to be the most important site for long-term carriage of E. coli O157:H7, and may serve as the source of bacteria found in the colon [Brown, C., et al. (1995) Vet. Pathol. 32:587. Histologic examination of colon tissue revealed no evidence of attachment of E. coli O157:H7 to colon tissue. Hence, the presence of E. coli O157:H7 in the colon appears to be a transient state whereby the bacteria are passing through, rather than colonizing the colon. Vaccines are not likely to be effective in reducing the amount of E. coli O157:H7 carried and shed by cattle.
The amount of E. coli O157:H7 carried by calves can be affected by nutrition and management practices. Rasmussen, et al. [(1993) FEMS Microbiol. Lett. 114:79-841 determined that E. coli O157:H7 grew unrestricted in rumen fluid collected from fasted cattle.
Some strains of E. coli can produce colicins that are inhibitory in vitro, to diarrheagenic E. coli strains, including strains of serotype O157:H7 [Bradley, D. E., et al. (1991) Can J. Microbiol. 37:97-104; Murinda, S. E., et al. (1996) Appl. Environ. Microbiol. 62:3196-3202]. Murinda et al. assayed twenty-four E. coli colicin-producing strains and determined that all E. coli O157:H7 strains evaluated were sensitive to Col E1 to E8, K and N on mitomycin-C-containing agar and also to Col G, Col. H and MccB17 on Luria agar. Patterns of colicin-sensitivity and resistance have been used for strain identification. Biological control of a bacterial strain based on its bacteriocin-sensitivity has not been achieved. However, Doyle, et al. U.S. Pat. No. 5,302,388, disclosed prevention or inhibition of Campylobacter jejuni colonization of poultry by administering a selected bacterial strain capable of competing with C. jejuni for colonization sites in poultry cecum and of inhibiting growth of C. jejuni.